1. Field of the Invention
The present invention relates to radio frequency (RF) transmitting material and structure combinations, and more particularly, to dual role structures capable of efficiently transmitting and receiving RF energy, and efficiently carrying and transmitting aerodynamic loads which occur on the primary load carrying structures of aircraft. RF transmitting materials having improved mechanical properties are combined with advanced structures technology to obtain efficient and low weight radar-tailored aerosurfaces and fuselage outer shell segment primary structures for use in a multitude of aircraft.
2. Discussion of the Prior Art
A significant portion of the present and future technology needed by such groups as the Department of Defense and NASA includes design, development and systems integration of mechanically and electrically efficient structures which serve as platforms for a variety of specialized electronic missions including Airborne Early Warning, Anti-Submarine Warfare, Electronic Warfare and military and civil surveillance. The increasing need for near future multi-mission platforms places increasing demands on the particular structure to not only carry primary and secondary aerodynamic loads efficiently, but to also transmit and receive RF energy with minimum losses.
The aircraft industry is a field in which the weight of any component and of any part that is utilized on an aircraft becomes an important factor in its design. In this particular field, it is also required that the stability and dimensional integrity of the aircraft remain constant. This means that in the case of an antenna system, the antenna system must be capable of taking up aerodynamic loads, accelerations on take-offs, launchings or the like and decelerations on landings. Specifically, such an antenna system has to remain stable with regard to any tendency toward deformation, for example, on account of low frequency oscillation.
In the past, antennas suitable for airborne radar or electronic applications were often mounted externally of the typical aerodynamic frame of an aircraft. These structures had to be of relatively heavy construction to withstand the aerodynamic forces of flight. As a result of the relatively high weight and interaction with the airstream of such structures, overall aircraft weight and flight performance were compromised. The design of antenna systems utilized by aircraft always involves a compromise of weight and size to avoid interference with aircraft aerodynamics. In addition, one does not want to interfere with the geometry of the aircraft.
More recently, antenna systems such as phased array antennas for improved scanning have been conformally integrated into airframe structures such as wings to improve aircraft performance while maintaining high radar efficiency. The prior art contains references which disclose the general concept of having antenna arrays housed within an aircraft surface. Included in this group of references are U.S. Pat. Nos. 4,186,400 and 4,514,734 both to Cermignani et al., 4,749,997 to Camonico, 4,116,405 to Bacchi et al. and 4,336,543 to Ganz et al., which specifically disclose the placement of antenna array elements along the leading edge of an aircraft wing. Additionally, U.S. Pat. Nos. 4,912,477 to Lory et al. and 4,872,016 to Kress disclose the placement or positioning of antenna elements within a horizontal stabilizer and fuselage structure. Although each of these references disclose conformal radar antenna systems, none of the references provide for conformal radar antenna systems to be placed or positioned within primary aerodynamic load carrying structures. The positioning of radar antenna systems within primary aerodynamic load carrying structures offers the advantage of a reduction in weight, the maximization of the structural efficiency of the aircraft and the maximization of the efficiency of the radar antenna system.
Presently, RF transmitting material/structures are restricted to non-primary or low level load carrying applications, as indicated by the above-cited prior art references, due to the material of construction which typically has low stiffness characteristics, and marginal strength. Weight penalties associated with the application of the current materials to primary aerodynamic load carrying structural applications is prohibitive. Therefore, new RF transmitting materials with significantly improved mechanical properties and novel design approaches are a critical need. These newer/emerging material systems have the potential to become efficient RF transmitting primary structures.